Ink-jet prints are often known for poor durability when exposed to water or high humidity. This results from the use of water-soluble and water dispersible colorants within the water-based ink. There has been great improvement in the area of water durability of ink-jet inks through incorporation of certain ink-jet compatible latex polymers. When printed as part of an ink-jet ink, a latex component of the ink can form a film on a media surface, entrapping and protecting at least some of the colorant within the hydrophobic print film. However, not all colorant will necessarily be protected upon printing, as would be optimal.
Polymers that form durable films are typically made from copolymers having bulk densities on the order of 1.15 g/cm3 or greater, which is appreciably greater than water, the primary component of thermal ink-jet ink. As such, conventional latex particles are normally designed to flocculate so that latex precipitate may be easily shaken or stirred back into dispersion without agglomeration. Such flocculation behavior is well known with latex paints. Unfortunately, these conventional teachings do not address the unique needs of ink-jet printing applications. For example, the micro-channel ink feeds in ink-jet pens are easily clogged with precipitant, particularly when a pen is stored or otherwise unused for prolonged periods of time. Such precipitation is not easily redispersed by pen shaking, as flow constriction prohibits adequate mixing within micro-channels of pen architecture. Additionally, micro-channels used for jetting can house some of the ink over prolonged periods in preparation for firing, and settled latex particulates can cause further constricting of the micro-channels. This can result in ink-jet pen failure due to clogging of the micro-channels. Further, the micron-order settling distances found in the fluid channels of thermal inkjet pens exacerbate the problem.